1. Field of the Invention
The present invention relates to an ultrasound imaging apparatus that scans a three-dimensional region and a method for generating an ultrasound image.
2. Description of the Related Art
Liver cancer accounts for approximately 10% of all cancer diseases, and the number has increased. A medical imaging apparatus such as an ultrasound imaging apparatus, an MRI apparatus and an X-ray CT apparatus is used for diagnosis of liver cancer. In particular, the diagnostic ability has increased in comparison with diagnosis with a two-dimensional image, because the thee-dimensional imaging method has been established in an X-ray CT apparatus and an MRI apparatus.
A method for treatment of liver cancer includes anticancer drug injection into hepatic artery, transcatheter arterial embolization (TAE), transcatheter arterial chemo-embolization (TACE), minimally invasive treatment, and laparotomy.
Among the abovementioned treatments, the minimally invasive treatment is applied particularly in many cases, because this treatment is technically simpler than the other methods and is less stressful for a patient. The minimally invasive treatment includes percutaneous ethanol injection technique (PEIT) and microwave ablation. These treatments are performed with a puncture. Treatment by the percutaneous ethanol injection technique is performed, while a puncture needle is monitored in real time with an ultrasound imaging apparatus, the position of the puncture needle is tracked and the position of the puncture needle is checked. Recently, as ablation treatment, radio frequency ablation (RFA) is often performed with a single needle or an expandable needle to expand to plural needles.
An ultrasound imaging apparatus capable of imaging a three-dimensional region is used for tracking the position of the puncture needle. In a case where a three-dimensional region is scanned with ultrasonic waves by using a 1D array probe in which a plurality of ultrasound transducers are arranged in a row in a predetermined direction (scanning direction), a 1D array probe provided with a swing mechanism is used (for example, Japanese Unexamined Patent Application Publication No. 2007-21018). The 1D array probe provided with a swing mechanism is capable of mechanically swinging the ultrasound transducers arranged in a row in the scanning direction, in a direction (swing direction) orthogonal to the scanning direction, thereby scanning a three-dimensional region with ultrasonic waves and acquiring volume data. The 1D array probe is provided with a motor for swinging the plurality of ultrasound transducers. The 1D array probe mechanically swings the ultrasound transducers in the swing direction by using the motor, thereby scanning a three-dimensional region and acquiring volume data.
By executing volume rendering on the volume data acquired by scan with ultrasonic waves, it is possible to generate three-dimensional image data representing a tissue within a subject and display a three-dimensional image based on the three-dimensional data. Further, by executing multi planar reconstruction on the volume data, it is possible to generate image data (MPR image data) at an arbitrary cross-section and display an MPR image based on the MPR image data.
In the conventional art, a puncture object (lesion) subjected to ablation treatment by a puncture needle and the puncture needle are included in a three-dimensional region scanned with ultrasonic waves, whereby three-dimensional image data representing the puncture object and the puncture needle is acquired. With reference to the three-dimensional image, the operator confirms the position of the puncture needle with respect to the puncture object and observes a process of puncture by the puncture needle.
In order that both the puncture object and the puncture needle are included in a three-dimensional scanning region, a maximum swing angle for swinging the ultrasound transducers is set, and a three-dimensional region defined by the maximum swing angle is scanned with ultrasonic waves. In other words, in order that both the puncture object and the puncture needle are included in a three-dimensional scanning region, the entire scanning region is scanned with ultrasonic waves.
In the 1D array prove having the swing mechanism as described above, a volume rate depends on the number of swings of the ultrasound transducer per unit time. In other words, the volume rate becomes higher as the number of swings per unit time increases, whereas the volume rate becomes lower as the number of swings decreases.
In order to observe a process of puncturing by the puncture needle with respect to the puncture object in the ablation treatment, it is required to track the position of the puncture needle in real time while acquiring and displaying an image in which the puncture object (lesion) is represented. For this, it is required to acquire and display a three-dimensional image or MPR image in which the puncture needle is represented in real time while acquiring and displaying a three-dimensional image or MPR image in which the puncture object is represented.
In the conventional art, the entire scanning region is scanned, so that it is possible to acquire and display an image in which a puncture object and a puncture needle are represented. However, the number of swings of the ultrasound transducer per unit time decreases, with the result that there is a problem that the volume rate becomes lower.
Consequently, it becomes difficult to acquire and display in real time a three-dimensional image or MPR image in which a puncture needle is represented, so that it is difficult to track the position of the puncture needle in real time.